Geographic Range

Historically, this species was found in most of the eastern United States. It was known from New Hampshire south and west to Pennsylvania and New Jersey, throughout the Appalachians, all of southeast down to the panhandle of Florida, west to eastern Texas, Oklahoma, Kansas and extreme southeastern Nebraska. Populations have also been found along the Mississippi drainage as far north as Minnesota, and in the Ohio River valley throughout southern Illinois and Indiana and extreme southern Ohio. This is the historic extent of the range, but the species has been extirpated in many areas, and populations are patchy and fragmented. (Conant and Collins, 1998)

Habitat

In the northern parts of their range, timber rattlesnakes live in forested rocky hills. In the southern parts of their range these snakes are found in uninhabited swampy areas. Crevices in rocky cliffs usually facing south or large boulders piled together make up the hibernating dens. (Brown, 1993)

Physical Description

Adult timber rattlesnakes range from 36-60 inches (90-152 cm) in length, and the record length for the species is 74.5 in. (189.2 cm). They exhibit sexual dimorphism; the males are larger, weighing around 2.0 lb. while the females weigh on an average 1.3 lb. There are several color morphs. The background color of the black morph is gray and the patterns are a rich, velvety black. The background color of the yellow morph is tan, the patterns are a sulfur yellow tinged brownish in patches. Western and southern populations have combinations of these two as well. All the snakes have transverse bands of color. The bands vary geographically; eastern, western, and southern types of timber rattlesnake are recognized. (Brown, 1993, Conant & Collins 1998) (Conant and Collins, 1998; Ernst and Ernst, 2003)

Reproduction

Males follow scent trails to find reproductively active females. Once a male finds a receptive female, he rubs the female's neck with his chin and places his body along hers. The male then rapidly jerks his head and body until he can move his cloaca under hers and insert his hemipenis. Copulation may last for several hours. Males may fight for access to a receptive female. (Ernst and Ernst, 2003)

Most mating occurs in the summer months, from mid-July to October. Females store sperm through the winter for use in the spring when they emerge from hibernation. Females begin the formation of eggs and yolk in the late summer and fall, those eggs then ovulate the following spring. The live young are born in the autumn, from August through October. Timber rattlesnakes are ovoviviparous, meaning that the eggs are incubated and hatched within the female and she gives birth to live, precocial young. Females give birth to 1 to 20 young, usually 6 to 10 (mean of 10.4). Litter size depends on the size of the female, with larger females having more young. Young are 19.5 to 38.3 cm long (mean 32.5), and weigh from 11.2 to 29.1 grams (mean 22.5). The young have similar patterns to adults, but tend to have a grayish hue. They have their first shedding at 7 to 10 days old, at which point they expose a button-like terminal scale where their rattle will eventually grow. Evn newborn young are dangerous, with fangs from 2.6 to 3.8 mm long and a supply of venom. (Ernst and Ernst, 2003)

Males become sexually mature at 4 to 6 years old; females mature at 7 to 13 years old. Males are mature at snout to vent lengths of 90 to 100 cm. Females are mature at snout to vent lengths of over 100 cm in C. h. atricaudatus and 67 to 90 cm in C. h. horridus. (Ernst and Ernst, 2003)

Female timber rattlesnakes invest significantly in pre-parturition nutrients and protection of their young. They give birth in birthing rookeries, which are often the same sites as winter hibernacula, and stay with the young for 7 to 10 days after birth. At that point the young disperse and become independent. (Ernst and Ernst, 2003)

Behavior

In the warmer months, timber rattlesnakes are lone predators. During the summer, the snakes are migratory. They roam several miles from their winter den and do not have a permanent home. They cannot tolerate winter and hibernate for up to 7 months each year, returning to the same den each year. They hibernate in dens which are often in rock crevices. These dens may accommodate 15-60 snakes.

The attack stance of rattlers is well-known. The snakes rise vertically with their head and neck forming an S, and when ready they thrust with fangs exposed. Another common behavior of rattlers is ritualized fighting among the males. It often occurs in the periods just before mating season. They lift their bodies and wrap themselves around each other, moving back and forth in a swaying motion, trying to pin each other down. (Brown, 1993)

Communication and Perception

Like the other snakes in the family Viperidae, timber rattlers are pit vipers. This means they have heat sensitive pit organs located between the nostrils and the eyes. They are sensitive to radiant energy and can distinguish very slight changes in temperature. (Ernst and Ernst, 2003)

Food Habits

Their main food source is small mammals, in particular mice, rats, squirrels, and rabbits. Birds are also sometimes killed. The prey is killed when bitten because the snake injects venom. Timber rattlesnakes wait until the animal is dead then swallows prey whole. (Ernst and Ernst, 2003)

Economic Importance for Humans: Negative

Conservation Status

Populations of timber snakes are rapidly being depleted across the species' range. The main causes are habitat destruction, snake hunting, and commercial collection for the pet trade. Several states have passed laws protecting the timber snake, but it is not on the threatened species list in many states. The species is not in serious danger but is headed in that direction unless efforts are made to protect it. (Brown, 1993)

Other Comments

While timber rattlesnakes are not aggressive and vicious, their venom is extremely strong. (Grzimek, 1975)

Contributors

Tanya Dewey (editor), Animal Diversity Web.

Ann Falk (author), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

hibernation

the state that some animals enter during winter in which normal physiological processes are significantly reduced, thus lowering the animal's energy requirements. The act or condition of passing winter in a torpid or resting state, typically involving the abandonment of homoiothermy in mammals.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

mountains

This terrestrial biome includes summits of high mountains, either without vegetation or covered by low, tundra-like vegetation.

native range

the area in which the animal is naturally found, the region in which it is endemic.

ovoviviparous

reproduction in which eggs develop within the maternal body without additional nourishment from the parent and hatch within the parent or immediately after laying.

polygynous

having more than one female as a mate at one time

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

venomous

an animal which has an organ capable of injecting a poisonous substance into a wound (for example, scorpions, jellyfish, and rattlesnakes).

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Brown, William S. 1993. Biology, Status, and Management of the Timber Rattlesnake (Crotalus horridus): A Guide for Conservation. Society for the Study of Amphibians and Reptiles, Oxford.

Disclaimer:
The Animal Diversity Web is an educational resource written largely by and for college students. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.

This material is based upon work supported by the
National Science Foundation
Grants DRL 0089283, DRL 0628151, DUE 0633095, DRL 0918590, and DUE 1122742. Additional support has come from the Marisla Foundation, UM College of Literature, Science, and the Arts, Museum of Zoology, and Information and Technology Services.